We are developing serologic assays for DNA base damage and are applying these assay systems to the study of base damage and repair in cells. Radiation damage to DNA is of primary importance to the understanding of radiation induced mutagenesis and carcinogenesis. The study of base damage has been difficult because chemical methods generally lack the sensitivity required to quantitate products in low yield which differ only slightly from the normal base. Serologic procedures are exceedingly promising since small quantities of product may be detected in the presence of high concentrations of precursor. Furthermore, measurement may be made with the intact DNA molecule, obviating hydrolysis of DNA and isolation and purification of the product. We have developed assays for several ionizing and UV radiation products (5-hydroxymethyl uridine, adenosine 1-N oxide, uridine, and thymine dimers) and for the normally occurring bases. The work will be extended to chemically altered bases. We employ phage neutralization assay, radioimmune assay, and fluorescence and immune radiography assays. BIBLIOGRAPHIC REFERENCES: Lewis, H.L., D.R. Muhleman, and J.F. Ward: Serologic assays for gamma-irradiated DNA base damage. (1976) Rad. Res. Soc. McConlogue, L.C., A. Norman, H.L. Lewis, and J.F. Ward: Serologic assays of pyrimidine dimer formation and repair. (1976) Rad. Res. Soc.